A Lever-Type PDMS Flexible Cavity for Acoustic Vector Sensor With High Sensitivity

The whispering gallery mode cavities with high quality factor as highly sensitive acoustic sensors, due to narrow linewidth, are capable of detecting slight external disturbances. However, spherical cavities pose a challenge in the directivity of acoustic detection caused by structure symmetry. Here, a lever acoustic sensor combined with flexible polymer cavity is proposed. The copper sheet as the acoustic signal receiver provides a good directivity. As a signal readout unit, the flexible characteristics of polymer cavity with the quality factor of 105 increase the signal response, which is fabricated by superoleophobic substrates. An optical fiber acts as a cantilever to transfer energy between them. Frequency responses and acoustic vibrations are collected between 200 Hz and 10 kHz in the experiment. The maximum sensitivity and the minimum detectable acoustic pressure at 4 kHz are 23.58 mV/Pa and 1.38 mPa/Hz $^{\text {1/2}}$ , respectively. The good directivity with a notch depth of 16 dB in the directional map is obtained, which shows a promising candidate for applications.